In most speaker systems, a vibrating diaphragm is mounted at an opening of a speaker enclosure. A common type of speaker enclosure is a sealed enclosure. In a sealed speaker enclosure, the diaphragm compresses air in the enclosure when it moves in and rarefies air when it moves out. In smaller speaker and enclosure designs, substantial back pressures are exerted against the vibrating diaphragm by the air within the enclosure. This back pressure retards the movement of the diaphragm and degrades the quality of the sound being reproduced. To effectively enlarge the volume of the speaker enclosure, the air within the enclosure can be replaced with a gas that is less dense than air.
However, with mobile devices, the barometric air pressure surrounding the speaker enclosure can decrease or increase abruptly, for example when the user is riding in an elevator. This will result in a net force being exerted on the diaphragm of the sealed speaker system, causing it to “stick” and therefore stop producing sound until the pressure inside the speaker has equalized with the barometer pressure (due to leakage). In air speaker systems, such barometric equalization is achieved relatively quickly (in order to prevent noticeable sticking of the diaphragm), by adding a small vent hole to the enclosure (at the expense of a small amount of sound quality degradation). This solution however will not work for an enclosure that is filled with gas and no air.